Field of the Invention
The present invention relates generally to Electric Vehicle Service Equipment (EVSE) and more particularly to a system and method for managing vehicle charging stations.
Description of the Prior Art
In most cases, a driver is not disposed to wait while an electric vehicle charges. A substantial portion of all vehicle charging will occur while the vehicle is parked for an extended period of time.
Large numbers of electric vehicles will promote the installation of large banks of electric vehicle service equipment (EVSE). EVSEs are commonly called “chargers”, even though this is not technically precise.
Even though large banks of EVSE are made available, and some or all of them might be occupied by an electric vehicle at a time, it can be the case that the aggregate demand for charging of the vehicles may exceed the amount of electric power available for use by the bank. This may be the case, for example, if the operator of the bank (e.g., an employer) has chosen to place a limit on how much electricity is supplied to the employees or guests in a building. Another example might find that the electrical service is completely adequate to operate all of the EVSE at full power, but during a load-shedding event, that capacity is artificially reduced by agreement between the power company and the operator of the bank. In still another example, whether or not the electrical service can support all the EVSE operating at full power, an operator may choose to limit the peak draw from the mains, so as not be classified as a certain kind of customer (i.e., one whose peak draw exceeds a particular value and under some tariffs can be charged higher rates for all power consumed).
Prior art systems control multiple EVSE to mitigate peak demand, but do not consider the timing requirement of individual drivers as stipulated by their requirements or expressed willingness to purchase additional electricity (i.e., charge) if the price is sufficiently low. Additionally, a system should be fair, that is, according to policy, it should operate in the short term on a first-come, first-served basis, but in the longer term, whatever electricity is available within the prescribed limits, should be made available to those needing it, or who are otherwise willing to purchase it. Individual preferences with respect to pricing should be respected, but an implementation should not differentially advantage or disadvantage individual drivers with respect to availability of electricity when the price is particularly low: All drivers should have equal (at least, statistically equal) access whenever the price is sufficiently low.